This invention relates generally to temperature indicating apparatus, and more particularly to apparatus for indicating at a visually accessible location remote from an object whether the temperature of that object is then at or has at some time exceeded a predetermined high temperature.
Generally, it is often necessary to monitor the temperature of objects which are not easily accessible either visually or physically. For example, circumstances frequently dictate that containers in which high temperature exothermic chemical reactions are to occur be located in areas outside the view of the general public, and for that matter other personnel such as technicians. Under such circumstances, it is necessary to periodically check these containers to ascertain whether the chemical reaction might have prematurely occurred. In such cases, such a check often necessitates time-consuming dismantling of, for example, wall panels or other structural elements behind which the object is located.
One example of such a case is in the periodic inspection required of so-called oxygen generating "candles" which are standard equipment on many airlines. Such candles generally comprise cylindrical containers housing appropriate chemicals, normally separated by a pressure-sensitive valve or diaphragm, which chemicals when reacted with each other produce oxygen. During this reaction, the surface temperature of the container often reaches a temperature of between 500.degree. and 600.degree. F.
In the past, tape has been applied to the container wall, which tape has been chemically treated so that its color changes at elevated temperatures. However, since these candles are mounted behind panel enclosures, a "tape check" is a time-consuming procedure involving removal of the panel, especially in view of the fact that some aircraft provide individual candles for each passenger seat.
Other prior art temperature indicators have proven to be not entirely satisfactory for a variety of reasons. Often, these indicators require outside power from batteries or other sources. Where the objects whose temperatures are to be monitored remain obscured from view for long periods of time (such as in the case of the oxygen generating candles discussed above), the temperature indicating apparatus should, most desirably, be completely self-contained, requiring no outside power for its operation. Further, other proposed temperature indicating apparatus have been found to be unsatisfactory due to their complexity and amount of labor involved in installation.
Additionally, any such apparatus should be relatively light, inexpensive, unobtrusive and tamper-proof, i.e. cannot be inadvertently reset after actuation.